The present invention is directed to a method and apparatus for controlling the amount of single face corrugated paper board web (hereinafter "single face web") passing through the bridge of a corrugator. In particular, the invention is directed to method and apparatus for regulating the length of single face web on the bridge by detecting the flutes of the single face web at the bridge inlet and outlet without using gear wheels, friction-driven rollers or similar mechanical components.
In U.S. Pat. No. 3,966,518, a bridge control is described wherein the flutes in a single face web are detected at the bridge inlet and outlet. Separate counts are maintained of the flutes passing the bridge inlet and outlet. The difference between the counts is utilized to vary the speed of the single facer machine so as to ensure uniform transit time per unit length of single face web through the bridge. It is suggested therein that the flutes can be counted using cog or gear wheels meshing with the flutes of the single face web. A cog or gear wheel which may be utilized in the control is disclosed, for example, in U.S. Pat. No. 3,104,997. The number and spacing of the teeth on the cog or gear wheel is chosen to match the flutes of the single face web. When two or more single face webs having different flute types are to be processed by the corrugator, separate gear wheels must be provided for each flute so that a multiplicity of wheels must be maintained. The operator must be sure to select the correct wheel for the particular flute in the single face web being run. Considerable operating time may be lost while the gear wheels are changed to match the flutes of the new single face web. Moreover, the operator may select the wrong wheel, and the mistake may not be noticed until the web has been damaged.
This problem is especially likely to be encountered in corrugators which have been retrofitted with single facers provided by different manufacturers. For example, one single facer (machine of a corrugator) may be replaced by a machine of a different manufacturer. The single face web produced by the substitute machine may differ only slightly in the number of flutes per unit length. The slight difference is likely to go unnoticed, and the operator may attempt to utilize the original cog or gear wheel to count the new single face flutes. The resultant error in the flute count may go unnoticed and provide erroneous results.
In U.S. Pat. No. 3,966,518, it is recognized that the flutes may be counted optically, but, to date no system has been proposed to do this. In fact, the corrugator described in U.S. Pat. No. 3,966,518 is not capable of exercising the desired control except where the flute sensors, such as the cog or gear wheels, are matched to the specific flute configuration of the single face web being run.
Conventionally, four flute configurations are utilized in the corrugated paperboard industry: A-flute having 33 to 35 flutes per foot with a depth of 0.185 inch; B-flute having 47 to 50 flutes per foot with a depth of 0.097 inch; C-flute having 37 to 39 flutes per foot with a depth of 0.142 inch; and E-flute having 90 to 96 flutes per foot and a depth of 0.045 inch.
An object of the present invention is to provide a control for the amount of single face web passing through the corrugator bridge which requires no cog or gear wheels, friction-drive rolls or the like.
Another object of the invention is to provide a control which can be adjusted to accomodate a wide variety of single face web flute configurations without any loss in operating time.
A further object of the invention is to provide a method and apparataus for maintaining the length of single face web on the corrugator bridge at an optimal level selectable by the operator.
Another object of the invention is to provide a flute counter which counts flutes without contact between the counter and the single face web.
A further object of the invention is to provide a bridge control wherein the length of single face web in the bridge can be maintained constant with extreme accuracy.
Other objects and advantages appear hereinafter.